The present invention relates to methods and apparatus for packaging products on a form-fill-seal system, and more particularly a method of cooling transverse seals formed on packages produced on form-fill-seal equipment.
It is well known, in packaging many goods including food items, to employ what is commonly known as form-fill-seal equipment. This equipment may be aligned in either a horizontal or vertical direction, with the flow path of rollstock film and a product to be packaged moving in essentially the same direction, either horizontally or in a downward vertical direction. In the vertical form-fill-seal arrangement, flexible packaging material is fed from a rollstock to a tube former where a tube is fashioned from the sheet material into a vertically dependent, upwardly open tube having overlapping longitudinal edges. These overlapping edges are subsequently sealed together longitudinally by means well known in the art and the end of the tube is sealed together by a pair of transverse or end heat seals which are vertically spaced apart. At this point the tube is filled with a measured quantity of the product to be packaged. A second heat sealing operation, typically performed after the filled tube has been downwardly advanced, completes enclosure of the product. Simultaneously with or shortly after the transverse heat sealing step, the tube is transversely severed by cutting means in a space between the vertically spaced apart pair of transverse heat seals. Thereafter the tube is downwardly advanced and the cycle is successively repeated so as to form a multiplicity of individually packaged products.
Alternatively, a single transverse heat seal including a pair of horizontally spaced apart sealing jaws may be used to form in effect two vertically adjacent heat seals which are simultaneously or subsequently severed at a line vertically intermittently the heat seals.
One particular vertical form-fill-seal arrangement utilizes, in addition to the transverse heat sealing and cutting means, a pair of squeezing rolls situated above the transverse heat sealing means. Such an arrangement is described for example in U.S. Pat. No. 4,506,494 issued to Shimoyama et al. The cutting means is described in this reference as also providing cooling for the just made transverse heat seals to cool and strengthen the seals soon after the sealing step is completed. The cooling-cutting means of this reference is situated a short distance beneath the heat sealing means, such that after the transverse heat sealing step is completed, the pair of squeezing rolls is rotated an increment corresponding to the heat seal width to bring the sealed portion of the tube in horizontal alignment with the cooling-cutting means. The cooling-cutting means is then activated to cool and severe the film in the seal area.
While this arrangement provides for a very satisfactory package, having strengthened heat seals, in some cases it is desirable to implement an alternative packaging arrangement using similar equipment to that described in the Shimoyama et al reference. This alternate method is desirable where for example higher packing speeds are required. In that event, a method somewhat similar to that described in FIGS. 3A-3D of the Shimoyama et al reference is employed. Thus, after transverse sealing, the filled package is drawn downward an entire package length, rather than the small increment preferred in the reference, before the cooling-cutting means is activated.
One problem that arises in the use of this alternate method is the strength of the heat seals immediately after the transverse heat sealing step has been completed. The just formed seal is required to bear the load of the filled package for a full package length of travel before the seal can be further cooled and the package severed. When heated food product for example in a liquid or viscous state is the product packaged in the film, the difficulty in forming a heat seal with adequate strength is further increased.
Various ideas have been proposed in the past for cooling transverse heat seals. For example, U.S. Pat. No. 4,532,753 issued to Kovacs discloses the use of air blown down on the just formed transverse seal to cool it, the air blown down from the vicinity of pinch rolls above the sealing members during initial opening of the sealing members and continuing generally until they reach their fully opened position. The disadvantage of such an arrangement in connection with vertical form fill seal equipment having separate sealing means and cooling-cutting means is that the seal traveling down from the seal area to the cooling-cutting area would actually be moving away from the air cooling apparatus, and the effectiveness of the cooling medium would thereby be reduced. An additional problem with the use of such an arrangement is that the air is being blown across the seal bars in order to reach the seal to be cooled, which is inefficient for proper heating and operation of the sealing means.
British Pat. No. 1,334,616 issued to DeGroot et al discloses an air cooling system in which, at the beginning of withdrawal of a pair of welding jaws, cooling air is blown against the newly formed seals through nozzles located immediately beneath the heating strips of the welding jaws and forming part of the welding component of the apparatus.
Also of interest is U.S. Pat. No. 3,340,129 issued to Grevich disclosing the use of cooling air discharged along apertures in a tube, and directed at the sealed area of a tubular film.
U.S. Pat. No. 4,571,926 issued to Scully discloses means for projecting jets of air downwardly against the front and back sides of a bag suspended in a forming device to assist in releasing the bag from the forming device when it is severed.
It is an object of the present invention to provide means for quickly cooling the transverse heat seals formed on a tubular film in a vertical form fill seal apparatus while the seal pouch is moving downwardly from a sealing means to a cutting means.
It is a further object of the present invention to provide such a cooling means and method for cooling the transverse seals such that the cooling medium contacts the seals in the seal area of the apparatus as well as during the downward movement of the sealed portion of the tubular film toward a cutting means located beneath the sealing means.